Re: FX-6300 fan won't go any higher than ~3500rpm.
Maximum fan speed can vary by OEM boxed fan provided. The fan speed will also change based on CPU temp/load unless you manually override it to run at a certain speed. You should however be able to adjust the fan speed to 100% or maximum in the BIOS and/or the Operating System. You may be required in some O/S's such as Win 10 to use a maximum performance "Power Plan" for both maximum fan speeds as well as proper use of ALL CPU cores.